In recent years, a technique for transferring larger amounts of data at a higher speed has been developed, and therefore a technique for saving the data is now being required. Further, the saving technique itself has been being developed, and therefore a magnetic material working as a bridge between both the techniques continues to be investigated.
As a magnetic material used for a coating-type magnetic recording medium, γ-iron oxide, chromium dioxide, a metal magnetic powder, and the like are widely used essentially. In addition, iron nitride (Fe16N2) and iron platinum (FePt) are being investigated recently.
In order to achieve magnetic recording with high density, there is a serious problem, which must be faced, of microparticulation of the magnetic material. Concerned researchers have intensively studied in an effort to form fine particles of the magnetic material and as a result, can provide a magnetic powder having a size smaller than a usually-conceivable size. However, in a case of a fine particle, in particular, a metallic magnetic powder mainly composed of a metal, there is an important problem of deterioration of magnetic characteristics caused by oxidation of the magnetic powder.
In order to solve the problem, use of a material which deteriorates less by oxidation as a material essentially constituting a magnetic powder may be exemplified as a countermeasure. Recently, a ferrite magnetic powder which includes iron oxide and deteriorates less by oxidation is attracted as one candidate of the next generation magnetic powders.
In such a situation, Patent Literatures 1 to 3 disclose a hexagonal crystal ferrite magnetic powder which includes fine particles and has high magnetic characteristics, and the powder is expected to be suitable for use in high-density magnetic recording.
Cited Literature 1 discloses a hexagonal crystal ferrite particle having a plate diameter and a plate thickness defined by geometric standard deviation, with a plate diameter of 18 to 30 nm, and an ordered particle shape. Patent Literature 2 discloses a particle having a plate diameter of 15 to 28 nm and particle size distribution defined by respective D70 and D50 values. Patent Literature 3 discloses a hexagonal crystal ferrite particle having defined particle diameter and BET value.